I'm coming at it solely on the basis of practical experience. Removing a single boilerplate check might seem insignificant, but it compounds: when these types are lightweight to work with you can extract more tiny helper functions, and then you have a whole vocabulary of common operations / ways of doing composition, and you can write these really readable functions that just get all the plumbing out the way (but without making it completely invisible) and let you focus on the business logic.